Facebook says it has removed 32 accounts and pages believed to have been set up to influence the mid-term US elections in November.
It said it was in the "very early" stages of the investigation and did not yet know who was behind the pages.
It said the account creators had gone to greater lengths to hide their identities than a Russia-based campaign to disrupt the US presidential vote.
It described attempts to erase election interference as an "arms race."
More to follow